What are the kinds of things that you like to see incorpotated into a science fiction wargame?

What kind of game mechanics, fluff, setting, themes etc draw you into to purchasing or playing a game do you like games that play up to certain tropes or are derivative of something else and how important is originality in the setting?

For me I love a rich well thought out universe or setting that the game is played out in, which is what originally drew me into 40k but equal important are the rules, to many special or unbalanced rules can really make the experience less than fun.